I wish I could give you a answer. I worked with these system a lot at GM. What I can confirm is you are not the only one to have a illuminated security light and nothing happening with the car.

You could be on the other side of the coin with these systems, a car that won't crank with no apparent activation of the security stytem.

The Factory Service Manual gives a good overview of the system complete with Body Control Module re-programing steps but it hasn't helped me solve the two conditions I have described.

You are not alone with this mystery light. Like I said it can get worse,with the car not cranking,we have many posts on this Forum with this problem with Passlock 2 systems. My only answer is that I still don't understand the sysyem sufficiently.

The simple scanner used by the auto stores won't pick up codes for anything like the security system. You would have to get the code(s) read by a GM dealer or an independent that had invested in a good code scanner that can read the non-generic manufacturer codes.

My understanding of when the light is on it indicates "activated"or "armed" not that a failure has been detected.

With the Ford PATS system your "THEFT" light will blink rapidly with key in "ignition" position when a fault is detected. There must be a illumination condition with the GM system that simply means "activated" and not indicating a fault.

Lots on the Web about Passlock 2. If the light comes on while driving your car is not protected by the Passlock system.

There is a Passlock module imbeded in the ignition lock cylinder. When you turn the key a signal is generated by the Hall effect system. A imbeded resistor sends or the BCM reads a signal and the signal must match a stored code or the starter is disabled.

There is also a lot of info how to bypass a malfunctioning system.

Earlier GM systems had this resistor embeded in the key.

Many Passlock 2 failures are from the passlock module (need to replace ignition lock cylinder) and from moisture in connections.

The Security light in my 2000 Blazer came on twice while I was driving it to and from work the other day. Both times it happened about 3 miles into the drive. No effect on driveability. I shut down and restarted the engine and that kept the light off for the remainder of the drive.

I disconnected the battery and the light has not come back on the last two days. All the Owner's Manual states, is that the Passlock system is disabled and to take it to a dealer.

I had the same problem with my 03 Impala when the door locks would not engage due to a blown fuse. The manuel is not really clear but when I replaced the fuse the light went out. Before I found the fuse, I would lock the doors manually and the security light went out as well. Do you have electric door locks? Do they work properly. Does the doors lock automatically when you shift into Reverse or Drive? I think it is tied to that system. The Security only means that there is something wrong with the door locking mechanisms I think.

My 03 Impala started blowing fuses on the door lock circuit and the security light would come on and engine not start, then the electric trunk release died. Finally replaced the Body Control Module (expensive) and everything resolved.